1. Field of the Invention
This invention relates to electrode materials for use in batteries, and electrodes and batteries using the same.
2. Description of the Related Art
In conventional polymer batteries, electrically conductive .pi.-conjugated polymers formed by electrochemical or chemical polymerization have been used as electrode materials. For example, the use of polyacetylene for electrodes was reported in J. Chem. Soc. Chem. Commun., (1981) 317-319. Thereafter, extensive investigations on polyaniline, polypyrrole, polythiophene and the like have been carried out, and books for the explanation of batteries using electrically conductive polymers have already been published.
However, when an electrically conductive .pi.-conjugated polymer alone is used, the resulting capacity is limited because of the reaction of 0.5 to 1 electron per monomeric unit.
Accordingly, in order to increase the capacity, it has been intended to fabricate a composite electrode by forming an electrically conductive .pi.-conjugated polymer by electrochemical or chemical polymerization and then adding thereto a quinone compound which has poor electronic conductivity but can induce an oxidation-reduction reaction. For example, a composite electrode formed from polyaniline and benzoquinone has been reported in Synth. Met., 83 (1996) 89-96. In this composite electrodes, the proportion of a part contributing to a oxidation-reduction reaction per molecular weight is increased, resulting in an increased capacity. The reason for this is that, while the use of an electrically conductive .pi.-conjugated polymer alone gives a low capacity because of the reaction of 0.5 to 1 electron per monomeric unit, the combined use of benzoquinone can add its oxidation-reduction capacity thereto. Moreover, the oxidation-reduction reaction of quinone proceeds rapidly as a result of interaction between the nitrogen atoms of polyaniline and benzoquinone, resulting in an enhanced power density.
However, batteries using such composite electrodes have the disadvantage that, as the number of charge-discharge cycles is increased, the quinone compound is eliminated to cause a decrease in capacity.
On the other hand, an electrode formed by adding an electrically conducting additive (e.g., carbon) to an unconjugated polymer having no electrical conductivity, such as an electrode using a polymer of benzoquinone as the unconjugated polymer, has been investigated. However, also with respect to batteries using such electrodes, it has been reported that, as the number of charge-discharge cycles is increased, the contact between the polymer and the electrically conducting additive is lost to cause a decrease in capacity.